WEST PALM BEACH, Fla. (AP) — Authorities are trying to determine whether any dangerous substance was contained in a white powder found in a letter at the Palm Beach County State Attorney’s Office.

Three people who work in or near the office’s mailroom were exposed to the substance Tuesday morning.

City spokesman Chase Scott says they’ve complained of headaches and nausea. The three workers were taken to the hospital along with a firefighter who reported possible cardiac problems.

An initial test on the substance was inconclusive. It’s been handed over to the FBI to analyze. Scott says that test could come back in the next day or two.

The mailroom remains off limits, but all other parts of the building are open.